This invention is directed toward a process for continuously forming low profile articles from thermoplastic material.
Systems for fabricating thermoplastic articles such as injection molding, compression molding, sheet thermoforming, profile extrusion and the like are known. Injection and compression molding systems are intermittent with respect to uninterrupted molding of the finished articles in that each requires a substantial finite portion of the total molding cycle for mold opening, closing and plastic charging steps which adversely impact formed article cost. In addition, substantial stresses are usually built into the fabricated articles because of the inherent nature of such processes in that at economically attractive molding cycles the plastic adjacent the mold surfaces cools more than that toward the center. Such stresses, amongst other adverse effects, frequently result in distortion of the articles on release of the constraining influence of the mold and/or later exposure to heat such as sunlight, hot liquids, elevated temperature contents and the like. Sheet thermoforming wherein a soft preshaped web is forcibly drawn into a mold cavity likewise inherently develops substantial stress levels in the formed articles and further is limited in maximum article thickness to approximately that of the initial sheet or less depending on the extent of draw. Profile extrusion though continuous is limited to shapes of constant cross section in the direction of extrusion. Embossing generally affects only the surface characteristics of the material being embossed and involves forcefully impressing a design on a continuous web without the capability of controllably locally varying the profile.